Physics-based audio and haptic synthesis

ABSTRACT

Disclosed herein are systems and methods for generating and presenting virtual audio for mixed reality systems. A method may include determining a collision between a first object and a second object, wherein the first object comprises a first virtual object. A memory storing one or more audio models can be accessed. It can be determined if the one or more audio models stored in the memory comprises an audio model corresponding to the first object. In accordance with a determination that the one or more audio models comprises an audio model corresponding to the first object, an audio signal can be synthesized, wherein the audio signal is based on the collision and the audio model corresponding to the first object, and the audio signal can be presented to a user via a speaker of a head-wearable device. In accordance with a determination that the one or more audio models does not comprise an audio model corresponding to the first object, an acoustic property of the first object can be determined, a custom audio model based on the acoustic property of the first object can be generated, an audio signal can be synthesized, wherein the audio signal is based on the collision and the custom audio model, and the audio signal can be presented, via a speaker of a head-wearable device, to a user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/951,657, filed Dec. 20, 2019, the contents of which isincorporated herein by reference in its entirety.

FIELD

This disclosure relates in general to systems and methods for presentingaudio and haptic signals, and in particular to systems and methods forpresenting audio and haptic signals to a user of a mixed realityenvironment.

BACKGROUND

Virtual environments are ubiquitous in computing environments, findinguse in video games (in which a virtual environment may represent a gameworld); maps (in which a virtual environment may represent terrain to benavigated); simulations (in which a virtual environment may simulate areal environment); digital storytelling (in which virtual characters mayinteract with each other in a virtual environment); and many otherapplications. Modern computer users are generally comfortableperceiving, and interacting with, virtual environments. However, users'experiences with virtual environments can be limited by the technologyfor presenting virtual environments. For example, conventional displays(e.g., 2D display screens) and audio systems (e.g., fixed speakers) maybe unable to realize a virtual environment in ways that create acompelling, realistic, and immersive experience.

Virtual reality (“VR”), augmented reality (“AR”), mixed reality (“MR”),and related technologies (collectively, “XR”) share an ability topresent, to a user of an XR system, sensory information corresponding toa virtual environment represented by data in a computer system. Suchsystems can offer a uniquely heightened sense of immersion and realismby combining virtual visual and audio cues with real sights and sounds.Accordingly, it can be desirable to present digital sounds to a user ofan XR system in such a way that the sounds seem to beoccurring—naturally, and consistently with the user's expectations ofthe sound—in the user's real environment. Generally speaking, usersexpect that virtual sounds will take on the acoustic properties of thereal environment in which they are heard. For instance, a user of an XRsystem in a large concert hall will expect the virtual sounds of the XRsystem to have large, cavernous sonic qualities; conversely, a user in asmall apartment will expect the sounds to be more dampened, close, andimmediate.

Existing technologies often fall short of these expectations, such as bypresenting virtual audio that does not take into account a user'ssurroundings, leading to feelings of inauthenticity that can compromisethe user experience. Observations of users of XR systems indicate thatwhile users may be relatively forgiving of visual mismatches betweenvirtual content and a real environment (e.g., inconsistencies inlighting); users may be more sensitive to auditory mismatches. Our ownauditory experiences, refined continuously throughout our lives, canmake us acutely aware of how our physical environments affect the soundswe hear; and we can be hyper-aware of sounds that are inconsistent withthose expectations. With XR systems, such inconsistencies can bejarring, and can turn an immersive and compelling experience into animplausible, imitative one. In extreme examples, auditoryinconsistencies can cause motion sickness and other ill effects as theinner ear is unable to reconcile auditory stimuli with theircorresponding visual cues.

Users of XR systems may expect to hear virtual sounds that correspond tovirtual objects generating the virtual sounds. In some cases, virtualsounds can be synthesized using recordings of real sounds that may bemixed together to produce a desired virtual sound. However, thisapproach suffers from several disadvantages. Using a database of realsounds may require a large amount of memory to store enough real soundsto produce a wide range of virtual sounds. In some cases, it may bedesirable to produce a virtual sound that does not have a correspondingreal sound (e.g., a recorded real sound that corresponds to the desiredvirtual sound may not exist) and that is sufficiently different fromreal sounds that the virtual sound may not be accurately synthesizedfrom real sounds. Accordingly, it can be desirable to develop a virtualaudio synthesis system that can produce a wide range of virtual soundsthat still have real acoustic properties that a user expects in avirtual sound.

BRIEF SUMMARY

Examples of the disclosure describe systems and methods for generatingand presenting virtual audio for mixed reality systems. According toexamples of the disclosure, a method may include determining a collisionbetween a first object and a second object, wherein the first objectcomprises a first virtual object. A memory storing one or more audiomodels can be accessed. It can be determined if the one or more audiomodels stored in the memory comprises an audio model corresponding tothe first object. In accordance with a determination that the one ormore audio models comprises an audio model corresponding to the firstobject, an audio signal can be synthesized, wherein the audio signal isbased on the collision and the audio model corresponding to the firstobject, and the audio signal can be presented to a user via a speaker ofa head-wearable device. In accordance with a determination that the oneor more audio models does not comprise an audio model corresponding tothe first object, an acoustic property of the first object can bedetermined, a custom audio model based on the acoustic property of thefirst object can be generated, an audio signal can be synthesized,wherein the audio signal is based on the collision and the custom audiomodel, and the audio signal can be presented, via a speaker of ahead-wearable device, to a user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrate an example mixed reality environment, accordingto some embodiments.

FIGS. 2A-2D illustrate components of an example mixed reality systemthat can be used to generate and interact with a mixed realityenvironment, according to some embodiments.

FIG. 3A illustrates an example mixed reality handheld controller thatcan be used to provide input to a mixed reality environment, accordingto some embodiments.

FIG. 3B illustrates an example auxiliary unit that can be used with anexample mixed reality system, according to some embodiments.

FIG. 4 illustrates an example functional block diagram for an examplemixed reality system, according to some embodiments.

FIG. 5 illustrates an example mixed reality environment, according tosome embodiments.

FIG. 6 illustrates an example virtual audio synthesis system, accordingto some embodiments.

FIG. 7 illustrates an example virtual audio synthesis system, accordingto some embodiments.

FIG. 8 illustrates an example process for choosing an audio model,according to some embodiments.

FIG. 9 illustrates an example process for generating an empirical audiomodel, according to some embodiments.

DETAILED DESCRIPTION

In the following description of examples, reference is made to theaccompanying drawings which form a part hereof, and in which it is shownby way of illustration specific examples that can be practiced. It is tobe understood that other examples can be used and structural changes canbe made without departing from the scope of the disclosed examples.

Mixed Reality Environment

Like all people, a user of a mixed reality system exists in a realenvironment—that is, a three-dimensional portion of the “real world,”and all of its contents, that are perceptible by the user. For example,a user perceives a real environment using one's ordinary human sensessight, sound, touch, taste, smell—and interacts with the realenvironment by moving one's own body in the real environment. Locationsin a real environment can be described as coordinates in a coordinatespace; for example, a coordinate can include latitude, longitude, andelevation with respect to sea level; distances in three orthogonaldimensions from a reference point; or other suitable values. Likewise, avector can describe a quantity having a direction and a magnitude in thecoordinate space.

A computing device can maintain, for example in a memory associated withthe device, a representation of a virtual environment. As used herein, avirtual environment is a computational representation of athree-dimensional space. A virtual environment can includerepresentations of any object, action, signal, parameter, coordinate,vector, or other characteristic associated with that space. In someexamples, circuitry (e.g., a processor) of a computing device canmaintain and update a state of a virtual environment; that is, aprocessor can determine at a first time to, based on data associatedwith the virtual environment and/or input provided by a user, a state ofthe virtual environment at a second time t1. For instance, if an objectin the virtual environment is located at a first coordinate at time t0,and has certain programmed physical parameters (e.g., mass, coefficientof friction); and an input received from user indicates that a forceshould be applied to the object in a direction vector; the processor canapply laws of kinematics to determine a location of the object at timet1 using basic mechanics. The processor can use any suitable informationknown about the virtual environment, and/or any suitable input, todetermine a state of the virtual environment at a time t1. Inmaintaining and updating a state of a virtual environment, the processorcan execute any suitable software, including software relating to thecreation and deletion of virtual objects in the virtual environment;software (e.g., scripts) for defining behavior of virtual objects orcharacters in the virtual environment; software for defining thebehavior of signals (e.g., audio signals) in the virtual environment;software for creating and updating parameters associated with thevirtual environment; software for generating audio signals in thevirtual environment; software for handling input and output; softwarefor implementing network operations; software for applying asset data(e.g., animation data to move a virtual object over time); or many otherpossibilities.

Output devices, such as a display or a speaker, can present any or allaspects of a virtual environment to a user. For example, a virtualenvironment may include virtual objects (which may includerepresentations of inanimate objects; people; animals; lights; etc.)that may be presented to a user. A processor can determine a view of thevirtual environment (for example, corresponding to a “camera” with anorigin coordinate, a view axis, and a frustum); and render, to adisplay, a viewable scene of the virtual environment corresponding tothat view. Any suitable rendering technology may be used for thispurpose. In some examples, the viewable scene may include only somevirtual objects in the virtual environment, and exclude certain othervirtual objects. Similarly, a virtual environment may include audioaspects that may be presented to a user as one or more audio signals.For instance, a virtual object in the virtual environment may generate asound originating from a location coordinate of the object (e.g., avirtual character may speak or cause a sound effect); or the virtualenvironment may be associated with musical cues or ambient sounds thatmay or may not be associated with a particular location. A processor candetermine an audio signal corresponding to a “listener” coordinate—forinstance, an audio signal corresponding to a composite of sounds in thevirtual environment, and mixed and processed to simulate an audio signalthat would be heard by a listener at the listener coordinate—and presentthe audio signal to a user via one or more speakers.

Because a virtual environment exists only as a computational structure,a user cannot directly perceive a virtual environment using one'sordinary senses. Instead, a user can perceive a virtual environment onlyindirectly, as presented to the user, for example by a display,speakers, haptic output devices, etc. Similarly, a user cannot directlytouch, manipulate, or otherwise interact with a virtual environment; butcan provide input data, via input devices or sensors, to a processorthat can use the device or sensor data to update the virtualenvironment. For example, a camera sensor can provide optical dataindicating that a user is trying to move an object in a virtualenvironment, and a processor can use that data to cause the object torespond accordingly in the virtual environment.

A mixed reality system can present to the user, for example using atransmissive display and/or one or more speakers (which may, forexample, be incorporated into a wearable head device), a mixed realityenvironment (“MRE”) that combines aspects of a real environment and avirtual environment. In some embodiments, the one or more speakers maybe external to the head-mounted wearable unit. As used herein, a MRE isa simultaneous representation of a real environment and a correspondingvirtual environment. In some examples, the corresponding real andvirtual environments share a single coordinate space; in some examples,a real coordinate space and a corresponding virtual coordinate space arerelated to each other by a transformation matrix (or other suitablerepresentation). Accordingly, a single coordinate (along with, in someexamples, a transformation matrix) can define a first location in thereal environment, and also a second, corresponding, location in thevirtual environment; and vice versa.

In a MRE, a virtual object (e.g., in a virtual environment associatedwith the MRE) can correspond to a real object (e.g., in a realenvironment associated with the MRE). For instance, if the realenvironment of a MRE includes a real lamp post (a real object) at alocation coordinate, the virtual environment of the MRE may include avirtual lamp post (a virtual object) at a corresponding locationcoordinate. As used herein, the real object in combination with itscorresponding virtual object together constitute a “mixed realityobject.” It is not necessary for a virtual object to perfectly match oralign with a corresponding real object. In some examples, a virtualobject can be a simplified version of a corresponding real object. Forinstance, if a real environment includes a real lamp post, acorresponding virtual object may include a cylinder of roughly the sameheight and radius as the real lamp post (reflecting that lamp posts maybe roughly cylindrical in shape). Simplifying virtual objects in thismanner can allow computational efficiencies, and can simplifycalculations to be performed on such virtual objects. Further, in someexamples of a MRE, not all real objects in a real environment may beassociated with a corresponding virtual object. Likewise, in someexamples of a MRE, not all virtual objects in a virtual environment maybe associated with a corresponding real object. That is, some virtualobjects may solely in a virtual environment of a MRE, without anyreal-world counterpart.

In some examples, virtual objects may have characteristics that differ,sometimes drastically, from those of corresponding real objects. Forinstance, while a real environment in a MRE may include a green,two-armed cactus—a prickly inanimate object—a corresponding virtualobject in the MRE may have the characteristics of a green, two-armedvirtual character with human facial features and a surly demeanor. Inthis example, the virtual object resembles its corresponding real objectin certain characteristics (color, number of arms); but differs from thereal object in other characteristics (facial features, personality). Inthis way, virtual objects have the potential to represent real objectsin a creative, abstract, exaggerated, or fanciful manner; or to impartbehaviors (e.g., human personalities) to otherwise inanimate realobjects. In some examples, virtual objects may be purely fancifulcreations with no real-world counterpart (e.g., a virtual monster in avirtual environment, perhaps at a location corresponding to an emptyspace in a real environment).

Compared to VR systems, which present the user with a virtualenvironment while obscuring the real environment, a mixed reality systempresenting a MRE affords the advantage that the real environment remainsperceptible while the virtual environment is presented. Accordingly, theuser of the mixed reality system is able to use visual and audio cuesassociated with the real environment to experience and interact with thecorresponding virtual environment. As an example, while a user of VRsystems may struggle to perceive or interact with a virtual objectdisplayed in a virtual environment—because, as noted above, a usercannot directly perceive or interact with a virtual environment—a userof a MR system may find it intuitive and natural to interact with avirtual object by seeing, hearing, and touching a corresponding realobject in his or her own real environment. This level of interactivitycan heighten a user's feelings of immersion, connection, and engagementwith a virtual environment. Similarly, by simultaneously presenting areal environment and a virtual environment, mixed reality systems canreduce negative psychological feelings (e.g., cognitive dissonance) andnegative physical feelings (e.g., motion sickness) associated with VRsystems. Mixed reality systems further offer many possibilities forapplications that may augment or alter our experiences of the realworld.

FIG. 1A illustrates an example real environment 100 in which a user 110uses a mixed reality system 112. Mixed reality system 112 may include adisplay (e.g., a transmissive display) and one or more speakers, and oneor more sensors (e.g., a camera), for example as described below. Thereal environment 100 shown includes a rectangular room 104A, in whichuser 110 is standing; and real objects 122A (a lamp), 124A (a table),126A (a sofa), and 128A (a painting). Room 104A further includes alocation coordinate 106, which may be considered an origin of the realenvironment 100. As shown in FIG. 1A, an environment/world coordinatesystem 108 (comprising an x-axis 108X, a y-axis 108Y, and a z-axis 108Z)with its origin at point 106 (a world coordinate), can define acoordinate space for real environment 100. In some embodiments, theorigin point 106 of the environment/world coordinate system 108 maycorrespond to where the mixed reality system 112 was powered on. In someembodiments, the origin point 106 of the environment/world coordinatesystem 108 may be reset during operation. In some examples, user 110 maybe considered a real object in real environment 100; similarly, user110's body parts (e.g., hands, feet) may be considered real objects inreal environment 100. In some examples, a user/listener/head coordinatesystem 114 (comprising an x-axis 114X, a y-axis 114Y, and a z-axis 114Z)with its origin at point 115 (e.g., user/listener/head coordinate) candefine a coordinate space for the user/listener/head on which the mixedreality system 112 is located. The origin point 115 of theuser/listener/head coordinate system 114 may be defined relative to oneor more components of the mixed reality system 112. For example, theorigin point 115 of the user/listener/head coordinate system 114 may bedefined relative to the display of the mixed reality system 112 such asduring initial calibration of the mixed reality system 112. A matrix(which may include a translation matrix and a Quaternion matrix or otherrotation matrix), or other suitable representation can characterize atransformation between the user/listener/head coordinate system 114space and the environment/world coordinate system 108 space. In someembodiments, a left ear coordinate 116 and a right ear coordinate 117may be defined relative to the origin point 115 of theuser/listener/head coordinate system 114. A matrix (which may include atranslation matrix and a Quaternion matrix or other rotation matrix), orother suitable representation can characterize a transformation betweenthe left ear coordinate 116 and the right ear coordinate 117, anduser/listener/head coordinate system 114 space. The user/listener/headcoordinate system 114 can simplify the representation of locationsrelative to the user's head, or to a head-mounted device, for example,relative to the environment/world coordinate system 108. UsingSimultaneous Localization and Mapping (SLAM), visual odometry, or othertechniques, a transformation between user coordinate system 114 andenvironment coordinate system 108 can be determined and updated inreal-time.

FIG. 1B illustrates an example virtual environment 130 that correspondsto real environment 100. The virtual environment 130 shown includes avirtual rectangular room 104B corresponding to real rectangular room104A; a virtual object 122B corresponding to real object 122A; a virtualobject 124B corresponding to real object 124A; and a virtual object 126Bcorresponding to real object 126A. Metadata associated with the virtualobjects 122B, 124B, 126B can include information derived from thecorresponding real objects 122A, 124A, 126A. Virtual environment 130additionally includes a virtual monster 132, which does not correspondto any real object in real environment 100. Real object 128A in realenvironment 100 does not correspond to any virtual object in virtualenvironment 130. A persistent coordinate system 133 (comprising anx-axis 133X, a y-axis 133Y, and a z-axis 133Z) with its origin at point134 (persistent coordinate), can define a coordinate space for virtualcontent. The origin point 134 of the persistent coordinate system 133may be defined relative/with respect to one or more real objects, suchas the real object 126A. A matrix (which may include a translationmatrix and a Quaternion matrix or other rotation matrix), or othersuitable representation can characterize a transformation between thepersistent coordinate system 133 space and the environment/worldcoordinate system 108 space. In some embodiments, each of the virtualobjects 122B, 124B, 126B, and 132 may have their own persistentcoordinate point relative to the origin point 134 of the persistentcoordinate system 133. In some embodiments, there may be multiplepersistent coordinate systems and each of the virtual objects 122B,124B, 126B, and 132 may have their own persistent coordinate pointrelative to one or more persistent coordinate systems.

With respect to FIGS. 1A and 1B, environment/world coordinate system 108defines a shared coordinate space for both real environment 100 andvirtual environment 130. In the example shown, the coordinate space hasits origin at point 106. Further, the coordinate space is defined by thesame three orthogonal axes (108X, 108Y, 108Z). Accordingly, a firstlocation in real environment 100, and a second, corresponding locationin virtual environment 130, can be described with respect to the samecoordinate space. This simplifies identifying and displayingcorresponding locations in real and virtual environments, because thesame coordinates can be used to identify both locations. However, insome examples, corresponding real and virtual environments need not usea shared coordinate space. For instance, in some examples (not shown), amatrix (which may include a translation matrix and a Quaternion matrixor other rotation matrix), or other suitable representation cancharacterize a transformation between a real environment coordinatespace and a virtual environment coordinate space.

FIG. 1C illustrates an example MRE 150 that simultaneously presentsaspects of real environment 100 and virtual environment 130 to user 110via mixed reality system 112. In the example shown, MRE 150simultaneously presents user 110 with real objects 122A, 124A, 126A, and128A from real environment 100 (e.g., via a transmissive portion of adisplay of mixed reality system 112); and virtual objects 122B, 124B,126B, and 132 from virtual environment 130 (e.g., via an active displayportion of the display of mixed reality system 112). As above, originpoint 106 acts as an origin for a coordinate space corresponding to MRE150, and coordinate system 108 defines an x-axis, y-axis, and z-axis forthe coordinate space.

In the example shown, mixed reality objects include corresponding pairsof real objects and virtual objects (i.e., 122A/122B, 124A/124B,126A/126B) that occupy corresponding locations in coordinate space 108.In some examples, both the real objects and the virtual objects may besimultaneously visible to user 110. This may be desirable in, forexample, instances where the virtual object presents informationdesigned to augment a view of the corresponding real object (such as ina museum application where a virtual object presents the missing piecesof an ancient damaged sculpture). In some examples, the virtual objects(122B, 124B, and/or 126B) may be displayed (e.g., via active pixelatedocclusion using a pixelated occlusion shutter) so as to occlude thecorresponding real objects (122A, 124A, and/or 126A). This may bedesirable in, for example, instances where the virtual object acts as avisual replacement for the corresponding real object (such as in aninteractive storytelling application where an inanimate real objectbecomes a “living” character).

In some examples, real objects (e.g., 122A, 124A, 126A) may beassociated with virtual content or helper data that may not necessarilyconstitute virtual objects. Virtual content or helper data canfacilitate processing or handling of virtual objects in the mixedreality environment. For example, such virtual content could includetwo-dimensional representations of corresponding real objects; customasset types associated with corresponding real objects; or statisticaldata associated with corresponding real objects. This information canenable or facilitate calculations involving a real object withoutincurring unnecessary computational overhead.

In some examples, the presentation described above may also incorporateaudio aspects. For instance, in MRE 150, virtual monster 132 could beassociated with one or more audio signals, such as a footstep soundeffect that is generated as the monster walks around MRE 150. Asdescribed further below, a processor of mixed reality system 112 cancompute an audio signal corresponding to a mixed and processed compositeof all such sounds in MRE 150, and present the audio signal to user 110via one or more speakers included in mixed reality system 112 and/or oneor more external speakers.

Example Mixed Reality System

Example mixed reality system 112 can include a wearable head device(e.g., a wearable augmented reality or mixed reality head device)comprising a display (which may include left and right transmissivedisplays, which may be near-eye displays, and associated components forcoupling light from the displays to the user's eyes); left and rightspeakers (e.g., positioned adjacent to the user's left and right ears,respectively); an inertial measurement unit (IMU)(e.g., mounted to atemple arm of the head device); an orthogonal coil electromagneticreceiver (e.g., mounted to the left temple piece); left and rightcameras (e.g., depth (time-of-flight) cameras) oriented away from theuser; and left and right eye cameras oriented toward the user (e.g., fordetecting the user's eye movements). However, a mixed reality system 112can incorporate any suitable display technology, and any suitablesensors (e.g., optical, infrared, acoustic, LIDAR, EOG, GPS, magnetic).In addition, mixed reality system 112 may incorporate networkingfeatures (e.g., Wi-Fi capability) to communicate with other devices andsystems, including other mixed reality systems. Mixed reality system 112may further include a battery (which may be mounted in an auxiliaryunit, such as a belt pack designed to be worn around a user's waist), aprocessor, and a memory. The wearable head device of mixed realitysystem 112 may include tracking components, such as an IMU or othersuitable sensors, configured to output a set of coordinates of thewearable head device relative to the user's environment. In someexamples, tracking components may provide input to a processorperforming a Simultaneous Localization and Mapping (SLAM) and/or visualodometry algorithm. In some examples, mixed reality system 112 may alsoinclude a handheld controller 300, and/or an auxiliary unit 320, whichmay be a wearable beltpack, as described further below.

FIGS. 2A-2D illustrate components of an example mixed reality system 200(which may correspond to mixed reality system 112) that may be used topresent a MRE (which may correspond to MRE 150), or other virtualenvironment, to a user. FIG. 2A illustrates a perspective view of awearable head device 2102 included in example mixed reality system 200.FIG. 2B illustrates a top view of wearable head device 2102 worn on auser's head 2202. FIG. 2C illustrates a front view of wearable headdevice 2102. FIG. 2D illustrates an edge view of example eyepiece 2110of wearable head device 2102. As shown in FIGS. 2A-2C, the examplewearable head device 2102 includes an example left eyepiece (e.g., aleft transparent waveguide set eyepiece) 2108 and an example righteyepiece (e.g., a right transparent waveguide set eyepiece) 2110. Eacheyepiece 2108 and 2110 can include transmissive elements through which areal environment can be visible, as well as display elements forpresenting a display (e.g., via imagewise modulated light) overlappingthe real environment. In some examples, such display elements caninclude surface diffractive optical elements for controlling the flow ofimagewise modulated light. For instance, the left eyepiece 2108 caninclude a left incoupling grating set 2112, a left orthogonal pupilexpansion (OPE) grating set 2120, and a left exit (output) pupilexpansion (EPE) grating set 2122. Similarly, the right eyepiece 2110 caninclude a right incoupling grating set 2118, a right OPE grating set2114 and a right EPE grating set 2116. Imagewise modulated light can betransferred to a user's eye via the incoupling gratings 2112 and 2118,OPEs 2114 and 2120, and EPE 2116 and 2122. Each incoupling grating set2112, 2118 can be configured to deflect light toward its correspondingOPE grating set 2120, 2114. Each OPE grating set 2120, 2114 can bedesigned to incrementally deflect light down toward its associated EPE2122, 2116, thereby horizontally extending an exit pupil being formed.Each EPE 2122, 2116 can be configured to incrementally redirect at leasta portion of light received from its corresponding OPE grating set 2120,2114 outward to a user eyebox position (not shown) defined behind theeyepieces 2108, 2110, vertically extending the exit pupil that is formedat the eyebox. Alternatively, in lieu of the incoupling grating sets2112 and 2118, OPE grating sets 2114 and 2120, and EPE grating sets 2116and 2122, the eyepieces 2108 and 2110 can include other arrangements ofgratings and/or refractive and reflective features for controlling thecoupling of imagewise modulated light to the user's eyes.

In some examples, wearable head device 2102 can include a left templearm 2130 and a right temple arm 2132, where the left temple arm 2130includes a left speaker 2134 and the right temple arm 2132 includes aright speaker 2136. An orthogonal coil electromagnetic receiver 2138 canbe located in the left temple piece, or in another suitable location inthe wearable head unit 2102. An Inertial Measurement Unit (IMU) 2140 canbe located in the right temple arm 2132, or in another suitable locationin the wearable head device 2102. The wearable head device 2102 can alsoinclude a left depth (e.g., time-of-flight) camera 2142 and a rightdepth camera 2144. The depth cameras 2142, 2144 can be suitably orientedin different directions so as to together cover a wider field of view.

In the example shown in FIGS. 2A-2D, a left source of imagewisemodulated light 2124 can be optically coupled into the left eyepiece2108 through the left incoupling grating set 2112, and a right source ofimagewise modulated light 2126 can be optically coupled into the righteyepiece 2110 through the right incoupling grating set 2118. Sources ofimagewise modulated light 2124, 2126 can include, for example, opticalfiber scanners; projectors including electronic light modulators such asDigital Light Processing (DLP) chips or Liquid Crystal on Silicon (LCoS)modulators; or emissive displays, such as micro Light Emitting Diode(μLED) or micro Organic Light Emitting Diode (μOLED) panels coupled intothe incoupling grating sets 2112, 2118 using one or more lenses perside. The input coupling grating sets 2112, 2118 can deflect light fromthe sources of imagewise modulated light 2124, 2126 to angles above thecritical angle for Total Internal Reflection (TIR) for the eyepieces2108, 2110. The OPE grating sets 2114, 2120 incrementally deflect lightpropagating by TIR down toward the EPE grating sets 2116, 2122. The EPEgrating sets 2116, 2122 incrementally couple light toward the user'sface, including the pupils of the user's eyes.

In some examples, as shown in FIG. 2D, each of the left eyepiece 2108and the right eyepiece 2110 includes a plurality of waveguides 2402. Forexample, each eyepiece 2108, 2110 can include multiple individualwaveguides, each dedicated to a respective color channel (e.g., red,blue and green). In some examples, each eyepiece 2108, 2110 can includemultiple sets of such waveguides, with each set configured to impartdifferent wavefront curvature to emitted light. The wavefront curvaturemay be convex with respect to the user's eyes, for example to present avirtual object positioned a distance in front of the user (e.g., by adistance corresponding to the reciprocal of wavefront curvature). Insome examples, EPE grating sets 2116, 2122 can include curved gratinggrooves to effect convex wavefront curvature by altering the Poyntingvector of exiting light across each EPE.

In some examples, to create a perception that displayed content isthree-dimensional, stereoscopically-adjusted left and right eye imagerycan be presented to the user through the imagewise light modulators2124, 2126 and the eyepieces 2108, 2110. The perceived realism of apresentation of a three-dimensional virtual object can be enhanced byselecting waveguides (and thus corresponding the wavefront curvatures)such that the virtual object is displayed at a distance approximating adistance indicated by the stereoscopic left and right images. Thistechnique may also reduce motion sickness experienced by some users,which may be caused by differences between the depth perception cuesprovided by stereoscopic left and right eye imagery, and the autonomicaccommodation (e.g., object distance-dependent focus) of the human eye.

FIG. 2D illustrates an edge-facing view from the top of the righteyepiece 2110 of example wearable head device 2102. As shown in FIG. 2D,the plurality of waveguides 2402 can include a first subset of threewaveguides 2404 and a second subset of three waveguides 2406. The twosubsets of waveguides 2404, 2406 can be differentiated by different EPEgratings featuring different grating line curvatures to impart differentwavefront curvatures to exiting light. Within each of the subsets ofwaveguides 2404, 2406 each waveguide can be used to couple a differentspectral channel (e.g., one of red, green and blue spectral channels) tothe user's right eye 2206. (Although not shown in FIG. 2D, the structureof the left eyepiece 2108 is analogous to the structure of the righteyepiece 2110.)

FIG. 3A illustrates an example handheld controller component 300 of amixed reality system 200. In some examples, handheld controller 300includes a grip portion 346 and one or more buttons 350 disposed along atop surface 348. In some examples, buttons 350 may be configured for useas an optical tracking target, e.g., for tracking six-degree-of-freedom(6DOF) motion of the handheld controller 300, in conjunction with acamera or other optical sensor (which may be mounted in a head unit(e.g., wearable head device 2102) of mixed reality system 200). In someexamples, handheld controller 300 includes tracking components (e.g., anIMU or other suitable sensors) for detecting position or orientation,such as position or orientation relative to wearable head device 2102.In some examples, such tracking components may be positioned in a handleof handheld controller 300, and/or may be mechanically coupled to thehandheld controller. Handheld controller 300 can be configured toprovide one or more output signals corresponding to one or more of apressed state of the buttons; or a position, orientation, and/or motionof the handheld controller 300 (e.g., via an IMU). Such output signalsmay be used as input to a processor of mixed reality system 200. Suchinput may correspond to a position, orientation, and/or movement of thehandheld controller (and, by extension, to a position, orientation,and/or movement of a hand of a user holding the controller). Such inputmay also correspond to a user pressing buttons 350.

FIG. 3B illustrates an example auxiliary unit 320 of a mixed realitysystem 200. The auxiliary unit 320 can include a battery to provideenergy to operate the system 200, and can include a processor forexecuting programs to operate the system 200. As shown, the exampleauxiliary unit 320 includes a clip 2128, such as for attaching theauxiliary unit 320 to a user's belt. Other form factors are suitable forauxiliary unit 320 and will be apparent, including form factors that donot involve mounting the unit to a user's belt. In some examples,auxiliary unit 320 is coupled to the wearable head device 2102 through amulticonduit cable that can include, for example, electrical wires andfiber optics. Wireless connections between the auxiliary unit 320 andthe wearable head device 2102 can also be used.

In some examples, mixed reality system 200 can include one or moremicrophones to detect sound and provide corresponding signals to themixed reality system. In some examples, a microphone may be attached to,or integrated with, wearable head device 2102, and may be configured todetect a user's voice. In some examples, a microphone may be attachedto, or integrated with, handheld controller 300 and/or auxiliary unit320. Such a microphone may be configured to detect environmental sounds,ambient noise, voices of a user or a third party, or other sounds.

FIG. 4 shows an example functional block diagram that may correspond toan example mixed reality system, such as mixed reality system 200described above (which may correspond to mixed reality system 112 withrespect to FIG. 1). As shown in FIG. 4, example handheld controller 400B(which may correspond to handheld controller 300 (a “totem”)) includes atotem-to-wearable head device six degree of freedom (6DOF) totemsubsystem 404A and example wearable head device 400A (which maycorrespond to wearable head device 2102) includes a totem-to-wearablehead device 6DOF subsystem 404B. In the example, the 6DOF totemsubsystem 404A and the 6DOF subsystem 404B cooperate to determine sixcoordinates (e.g., offsets in three translation directions and rotationalong three axes) of the handheld controller 400B relative to thewearable head device 400A. The six degrees of freedom may be expressedrelative to a coordinate system of the wearable head device 400A. Thethree translation offsets may be expressed as X, Y, and Z offsets insuch a coordinate system, as a translation matrix, or as some otherrepresentation. The rotation degrees of freedom may be expressed assequence of yaw, pitch and roll rotations, as a rotation matrix, as aquaternion, or as some other representation. In some examples, thewearable head device 400A; one or more depth cameras 444 (and/or one ormore non-depth cameras) included in the wearable head device 400A;and/or one or more optical targets (e.g., buttons 350 of handheldcontroller 400B as described above, or dedicated optical targetsincluded in the handheld controller 400B) can be used for 6DOF tracking.In some examples, the handheld controller 400B can include a camera, asdescribed above; and the wearable head device 400A can include anoptical target for optical tracking in conjunction with the camera. Insome examples, the wearable head device 400A and the handheld controller400B each include a set of three orthogonally oriented solenoids whichare used to wirelessly send and receive three distinguishable signals.By measuring the relative magnitude of the three distinguishable signalsreceived in each of the coils used for receiving, the 6DOF of thewearable head device 400A relative to the handheld controller 400B maybe determined. Additionally, 6DOF totem subsystem 404A can include anInertial Measurement Unit (IMU) that is useful to provide improvedaccuracy and/or more timely information on rapid movements of thehandheld controller 400B.

In some examples, it may become necessary to transform coordinates froma local coordinate space (e.g., a coordinate space fixed relative to thewearable head device 400A) to an inertial coordinate space (e.g., acoordinate space fixed relative to the real environment), for example inorder to compensate for the movement of the wearable head device 400Arelative to the coordinate system 108. For instance, suchtransformations may be necessary for a display of the wearable headdevice 400A to present a virtual object at an expected position andorientation relative to the real environment (e.g., a virtual personsitting in a real chair, facing forward, regardless of the wearable headdevice's position and orientation), rather than at a fixed position andorientation on the display (e.g., at the same position in the rightlower corner of the display), to preserve the illusion that the virtualobject exists in the real environment (and does not, for example, appearpositioned unnaturally in the real environment as the wearable headdevice 400A shifts and rotates). In some examples, a compensatorytransformation between coordinate spaces can be determined by processingimagery from the depth cameras 444 using a SLAM and/or visual odometryprocedure in order to determine the transformation of the wearable headdevice 400A relative to the coordinate system 108. In the example shownin FIG. 4, the depth cameras 444 are coupled to a SLAM/visual odometryblock 406 and can provide imagery to block 406. The SLAM/visual odometryblock 406 implementation can include a processor configured to processthis imagery and determine a position and orientation of the user'shead, which can then be used to identify a transformation between a headcoordinate space and another coordinate space (e.g., an inertialcoordinate space). Similarly, in some examples, an additional source ofinformation on the user's head pose and location is obtained from an IMU409. Information from the IMU 409 can be integrated with informationfrom the SLAM/visual odometry block 406 to provide improved accuracyand/or more timely information on rapid adjustments of the user's headpose and position.

In some examples, the depth cameras 444 can supply 3D imagery to a handgesture tracker 411, which may be implemented in a processor of thewearable head device 400A. The hand gesture tracker 411 can identify auser's hand gestures, for example by matching 3D imagery received fromthe depth cameras 444 to stored patterns representing hand gestures.Other suitable techniques of identifying a user's hand gestures will beapparent.

In some examples, one or more processors 416 may be configured toreceive data from the wearable head device's 6DOF headgear subsystem404B, the IMU 409, the SLAM/visual odometry block 406, depth cameras444, and/or the hand gesture tracker 411. The processor 416 can alsosend and receive control signals from the 6DOF totem system 404A. Theprocessor 416 may be coupled to the 6DOF totem system 404A wirelessly,such as in examples where the handheld controller 400B is untethered.Processor 416 may further communicate with additional components, suchas an audio-visual content memory 418, a Graphical Processing Unit (GPU)420, and/or a Digital Signal Processor (DSP) audio spatializer 422. TheDSP audio spatializer 422 may be coupled to a Head Related TransferFunction (HRTF) memory 425. The GPU 420 can include a left channeloutput coupled to the left source of imagewise modulated light 424 and aright channel output coupled to the right source of imagewise modulatedlight 426. GPU 420 can output stereoscopic image data to the sources ofimagewise modulated light 424, 426, for example as described above withrespect to FIGS. 2A-2D. The DSP audio spatializer 422 can output audioto a left speaker 412 and/or a right speaker 414. The DSP audiospatializer 422 can receive input from processor 419 indicating adirection vector from a user to a virtual sound source (which may bemoved by the user, e.g., via the handheld controller 320). Based on thedirection vector, the DSP audio spatializer 422 can determine acorresponding HRTF (e.g., by accessing a HRTF, or by interpolatingmultiple HRTFs). The DSP audio spatializer 422 can then apply thedetermined HRTF to an audio signal, such as an audio signalcorresponding to a virtual sound generated by a virtual object. This canenhance the believability and realism of the virtual sound, byincorporating the relative position and orientation of the user relativeto the virtual sound in the mixed reality environment—that is, bypresenting a virtual sound that matches a user's expectations of whatthat virtual sound would sound like if it were a real sound in a realenvironment.

In some examples, such as shown in FIG. 4, one or more of processor 416,GPU 420, DSP audio spatializer 422, HRTF memory 425, and audio/visualcontent memory 418 may be included in an auxiliary unit 400C (which maycorrespond to auxiliary unit 320 described above). The auxiliary unit400C may include a battery 427 to power its components and/or to supplypower to the wearable head device 400A or handheld controller 400B.Including such components in an auxiliary unit, which can be mounted toa user's waist, can limit the size and weight of the wearable headdevice 400A, which can in turn reduce fatigue of a user's head and neck.

While FIG. 4 presents elements corresponding to various components of anexample mixed reality system, various other suitable arrangements ofthese components will become apparent to those skilled in the art. Forexample, elements presented in FIG. 4 as being associated with auxiliaryunit 400C could instead be associated with the wearable head device 400Aor handheld controller 400B. Furthermore, some mixed reality systems mayforgo entirely a handheld controller 400B or auxiliary unit 400C. Suchchanges and modifications are to be understood as being included withinthe scope of the disclosed examples.

Virtual Sound Synthesis

Virtual sounds can be an important part of creating and/or maintainingan immersive MR experience. A MR experience may include virtual objectsinteracting with real objects and/or virtual objects interacting withother virtual objects. In these interactions, it may be appropriate togenerate virtual audio to accompany visual displays of virtual content.For example, a user may hold a virtual object (e.g., a virtual coffeemug) which may be visually and/or haptically presented to the user. Asthe user sets the virtual object down on a surface (e.g., a virtualand/or a real table), the user may expect to hear an accompanyingvirtual sound that reflects a contact between the virtual object and thevirtual and/or real surface. In some embodiments, a virtual sound caninclude a physical sound (e.g., a sound produced by one or more speakersthat may be presented to a user). In some embodiments, the virtual soundcan correspond to a real and/or virtual event (e.g., a collision betweena virtual and a real and/or virtual object) that a user may expect toproduce a sound. In some embodiments, an object can be an entirely realobject or an entirely virtual object (e.g., it exists only within one ormore computing systems). In some embodiments, an object can include bothreal and virtual components. For example, an object may include a realgeometry and a virtual pattern. In some embodiments, the object may bedisplayed to a user such that the object appears to have the realgeometry and the virtual pattern. To ensure an immersive MR experiencethat seamlessly blends virtual content with real content, the virtualsound accompanying the contact may be associated with certain acousticproperties. For example, the accompanying sound may be a function of oneor more materials of the virtual object. The accompanying sound may alsobe a function of one or more materials of the virtual and/or realsurface. In some embodiments, the accompanying sound may be a functionof the virtual object's geometry. In some embodiments, the accompanyingsound may be a function of a geometry of the virtual and/or realsurface. In some embodiments, the accompanying sound may be a functionof a real environment (e.g., a room) including the virtual and/or realsurface. It may be desirable to produce an accompanying virtual soundthat reflects a user's expectation based on their experience with realobjects (e.g., the accompanying virtual sound may sound like a realceramic material contacting a real wooden material). Sound effects, suchas the accompanying sound, may be presented to a user via one or morespeakers, for example, in a left speaker (e.g., left speaker 2134)and/or a right speaker (e.g., right speaker 2136).

Similar principles may also be applied to haptic effects. In someembodiments, low frequency signals may generally be considered hapticeffects (e.g., signals with frequencies below approximately 20 Hz). Insome cases, interactions between virtual objects and other virtualobjects or virtual objects and real objects may have an accompanyinghaptic effect. Like the virtual sounds described above, it may bedesirable to produce a haptic effect that approximates a haptic effectthat a user might expect based on the user's experience with realobjects. For example, a MR user setting a virtual coffee mug down on avirtual and/or surface may expect to feel a haptic effect correspondingto a real ceramic object being set down on a real wooden surface. Hapticeffects may be a function of one or more materials of the virtualobject. In some embodiments, haptic effects may be a function of one ormore materials of the virtual and/or real surface. In some embodiments,haptic effects may be a function of the virtual object's geometry. Insome embodiments, haptic effects may be a function of a geometry of thevirtual and/or real surface. Haptic effects may be presented to a uservia a transducer (e.g., a vibration motor), for example, in a handheldinterface device (e.g., handheld controller 300).

Virtual sounds and/or haptic effects can be generated in several ways.One method of generation includes one or more databases with prerecordedand/or pre-generated audio samples (e.g., .WAV files). The audio samplesmay be presented to the user (e.g., by playing the audio samples througha speaker or sending the audio samples to a transducer). In someembodiments, the audio samples may be mixed with other audio samplesbefore being presented to the user. Although it may be computationallyefficient to present virtual sounds and/or haptic effects usingprerecorded and/or pre-generated audio samples, this method can haveseveral disadvantages. One disadvantage may be that a large amount ofmemory may be used to store the prerecorded and/or pre-generated audiosamples. A MR system may present a wide range of visual virtual contentto a user, which may have a wide range of corresponding audio virtualcontent. For example, virtual objects may collide with, scrape against,rub against, and/or bounce on other virtual and/or real objects. Virtualand/or real objects may also diffract, diffuse, occlude, resonate,and/or absorb virtual sound. In some embodiments, each type of possibleinteraction between virtual objects and other virtual and/or realobjects may require a separate prerecorded and/or pre-generated audiosample. In some embodiments, materials involved in collisions betweenvirtual objects and virtual and/or real objects may be reflected in thevirtual audio. For example, contact between two ceramic objects maysound different than contact between a ceramic object and a woodenobject. Prerecorded and/or pre-generated audio samples may havedifferent versions of audio samples according to different materials andmaterial combinations, further increasing the storage used for thismethod of audio generation.

Another disadvantage of using prerecorded and/or pre-generated audiosamples is that the generated virtual audio may be limited to theexisting audio samples and/or combinations of those audio samples. Insome embodiments, it may be desirable to generate virtual audio that maynot be producible using existing audio samples and/or combinations ofthose audio samples. For example, a virtual object may be made out of afictional material called “vibranium,” which may have acousticproperties that differ from acoustic properties of real materials. Insome embodiments, the virtual object may clash against other virtualand/or real objects, and it may be desirable to produce a virtual soundto accompany the visual contact. Prerecorded and/or pre-generated audiosamples may not include an audio sample suitable for generating avirtual sound associated with vibranium. In some embodiments, it may bedesirable to generate virtual audio for objects that may not exist inthe real world. For example, a virtual object may be a “flutar,” whichmay be a fictional musical instrument with acoustic properties of both aflute and a guitar. In some embodiments, a user may play a virtualflutar, and it may be desirable to generate virtual sound that hasacoustic characteristics of both a real flute and a real guitar.

It can therefore be advantageous to develop a virtual audio synthesissystem that can produce a wide range of virtual sounds that still havereal acoustic properties that a user expects in a virtual sound. In someembodiments, virtual audio may be synthesized “on-the-fly,” usingdigital foley. Digital foley may include synthesizing virtual audio“from scratch” (e.g., synthesizing virtual audio without usingprerecorded and/or pre-generated audio samples). In some embodiments, asynthesized virtual sound can represent compressions and/or rarefactionsof air occurring at a user's left and/or right ear as if theinteractions of virtual and/or real objects occurred with equivalentreal objects. In some embodiments, a virtual audio synthesis system caninclude modeling physical characteristics of virtual and/or real objects(e.g., geometry, material composition, and the like), modeling collisionphysics (e.g., impact forces, resonation, and the like), and/orparametrically synthesizing virtual audio using physical and/ornon-physical parameters.

FIG. 5 illustrates an exemplary mixed reality environment, according tosome embodiments. Mixed reality environment (“MRE”) 502 (which cancorrespond to MRE 150) can include one or more virtual objects and oneor more real objects. In some embodiments, one or more virtual objectsmay interact with one or more real objects and/or one or more virtualobjects within MRE 502. For example, virtual ball 508 may bounce off ofreal floor 504 along path 510. In some embodiments, it may be desirableto present a virtual sound (e.g., a “thunk”) to accompany the visualcontact between virtual ball 508 and real floor 504 at contact point512. To maintain an immersive mixed reality experience, it may bedesirable to synthesize the virtual sound to reflect acousticcharacteristics that a user may expect to hear when a real ball (e.g., asoccer ball) bounces on a real floor (e.g., a wooden floor). Forexample, synthesizing the virtual audio may include identifying and/oraccounting for a material of real floor 504, a material of virtual ball508, a speed of virtual ball 508, a mass of virtual ball 508, a geometryof virtual ball 508, a surface area of virtual ball 508, a volume ofvirtual ball 508, a geometry of real floor 504, and/or other factors.

In some embodiments, one or more virtual objects in MRE 502 may interactwith other virtual objects in MRE 502. For example, virtual knight 516may wield a virtual sword 520, while virtual villain 514 may wield avirtual sword 518. While virtual knight 516 is fighting virtual villain514, virtual swords 520 and 518 may collide. It may be desirable toproduce a “clang” virtual sound upon collision. In some embodiments,synthesizing the virtual sound can account for a mass of each virtualsword, a material composition of each virtual sword, a speed of eachvirtual sword, a geometry of each virtual sword, and/or other factors.In some embodiments, synthesizing virtual audio using physics-basedmodels can produce virtual audio that may be indistinguishable fromsounds of real objects interacting with other real objects. In someembodiments, synthesizing the virtual sound can account for material ofreal floor 504, a geometry of real floor 504, properties of aroom/environment (including virtual knight 516 and virtual villain 514),and/or other factors.

In some embodiments, virtual audio synthesis system may account foracoustic properties of a virtual and/or real environment. A virtualand/or real environment may affect characteristics a user expects of avirtual sound by affecting how a virtual sound propagates through thevirtual and/or real environment. For example, a large, cavernous virtualand/or real environment with many hard surfaces may lead a user toexpect virtual sounds to produce significant echoes. A small virtualand/or real environment with significant cushioning/dampening may lead auser to expect muted virtual sounds. In some embodiments, physicaland/or perceptually relevant properties can include acoustic propertieslike a reverberation time, reverberation delay, and/or reverberationgain. A reverberation time may include a length of time required for asound to decay by a certain amount (e.g., by 60 decibels). Sound decaycan be a result of sound reflecting off surfaces in a real environment(e.g., walls, floors, furniture, etc.) whilst losing energy due to, forexample, sound absorption by a room's boundaries (e.g., walls, floors,ceiling, etc.), objects inside the room (e.g., chairs, furniture,people, etc.), and/or the air in the room. A reverberation time can beinfluenced by environmental factors. For example, absorbent surfaces(e.g., cushions) may absorb sound, and a reverberation time may bereduced as a result. In some embodiments, it may not be necessary tohave information about an original source to estimate an environment'sreverberation time. A reverberation gain can include a ratio of asound's direct/source/original energy to the sound's reverberationenergy (e.g., energy of a reverberation resulting from thedirect/source/original sound) where a listener and the source aresubstantially co-located (e.g., a user may clap their hands, producing asource sound that may be considered substantially co-located with one ormore microphones mounted on a head-wearable MR system). For example, animpulse (e.g., a clap) may have an energy associated with the impulse,and the reverberation sound from the impulse may have an energyassociated with the reverberation of the impulse. The ratio of theoriginal/source energy to the reverberation energy may be areverberation gain. A real environment's reverberation gain may beinfluenced by, for example, absorbent surfaces that can absorb sound andthereby reduce a reverberation energy. Other physically and/orperceptually relevant can include location-dependent magnitude and/orphase responses, absorption coefficients, impulse responses, and/orenergy decay relief.

FIG. 6 illustrates an exemplary virtual audio synthesis system,according to some embodiments. Virtual audio synthesis system 602 caninclude one or more computer systems configured to execute instructionsand/or store one or more data structures. For example, instructionsexecuted by virtual audio synthesis system 602 may be a process, whichmay run in a run-time environment. In some embodiments, instructionsexecuted by virtual audio synthesis system 602 can be a sub-process of aparent process. In some embodiments, instructions executed by virtualaudio synthesis system can be a thread of a parent process. In someembodiments, instructions executed by virtual audio synthesis system 602can operate as a service (e.g., as a background operating systemservice). In some embodiments, instructions executed by virtual audiosynthesis system 602 can continually run (e.g., in the background) whilean operating system of a MR system is running. In some embodiments,instructions executed by virtual audio synthesis system 602 can be aninstantiation of a parent background service, which may serve as a hostprocess to one or more background processes and/or sub-processes. Insome embodiments, instructions executed by virtual audio synthesissystem 602 can be part of an operating system of a MR system. In someembodiments, instructions executed by virtual audio synthesis system 602and/or data structures stored in virtual audio synthesis system 602 canbe accessible to applications that may run on the MR system. In someembodiments, a process (e.g., a process managed by a third-partyapplication) may request that a virtual sound be presented. Such arequest may take any suitable form. In some embodiments, a request thata virtual sound be presented can include a software instruction topresent the virtual sound; in some embodiments, such a request may behardware-driven. Requests may be issued with or without userinvolvement. Further, such requests may be received via local hardware(e.g., from the MR system itself), via external hardware (e.g., aseparate computer system in communication with the MR system), via theinternet (e.g., via a cloud server), or via any other suitable source orcombination of sources. Virtual audio synthesis system 602 and/or aparent background service (e.g., a parent audio rendering service) mayreceive this request (e.g., because virtual audio synthesis system 602may be listening in the background for such requests), and virtual audiosynthesis system 602 may synthesize a virtual sound. In someembodiments, a process may directly communicate with virtual audiosynthesis system 602 (e.g., via an API). In some embodiments, virtualaudio synthesis system 602 can provide a synthesized virtual sound toother processes, threads, and/or services (e.g., a synthesized virtualsound may be passed to a rendering engine).

In some embodiments, virtual audio synthesis system 602 may include oneor more modules (e.g., modules 604, 606, and 608), which may becomponents of virtual audio synthesis system 602. In some embodiments, amodule can include one or more computer systems configured to executeinstructions and/or store one or more data structures. For example,instructions executed by a module can be a process and/or sub-processrunning within virtual audio synthesis system 602. In some embodiments,instructions executed by a module can be a thread running within virtualaudio synthesis system 602. In some embodiments, instructions executedby a module may run within the same process address space and/or memoryspace as other components of virtual audio synthesis system 602. In someembodiments, instructions executed by a module may run in a differentprocess address space and/or memory space as other components of virtualaudio synthesis system 602. In some embodiments, instructions executedby a module may run on different hardware than other components ofvirtual audio synthesis system 602. For example, instructions executedby one or more modules of virtual audio synthesis system 602 may run onan audio-specific processor (e.g., a DSP), while other components ofvirtual audio synthesis system 602 may run on a general-purposeprocessor. In some embodiments, instructions executed by one or moremodules of virtual audio synthesis system 602 may be instantiated withinvirtual audio synthesis system 602. In some embodiments, instructionsexecuted by and/or data structures stored in modules within virtualaudio synthesis system 602 may communicate with other components ofvirtual audio synthesis system 602 (e.g., with instructions executed byand/or data structures stored in other modules).

In some embodiments, virtual audio synthesis system 602 may include oneor more modules and the one or more modules may include one or moresub-modules. In some embodiments, a sub-module can include one or morecomputer systems configured to execute instructions and/or store one ormore data structures. For example, instructions executed by a sub-modulecan be a process and/or sub-process running within virtual audiosynthesis system 602. In some embodiments, instructions executed by asub-module can be a thread running within virtual audio synthesis system602. In some embodiments, instructions executed by a sub-module may runwithin the same process address space and/or memory space as othercomponents of virtual audio synthesis system 602. In some embodiments,instructions executed by a sub-module may run in a different processaddress space and/or memory space as other components of virtual audiosynthesis system 602. In some embodiments, instructions executed by asub-module may run on different hardware than other components ofvirtual audio synthesis system 602. For example, instructions executedby one or more sub-modules of virtual audio synthesis system 602 may runon an audio-specific processor (e.g., a DSP), while other components ofvirtual audio synthesis system 602 may run on a general-purposeprocessor. In some embodiments, instructions executed by one or moresub-modules of virtual audio synthesis system 602 may be instantiatedwithin virtual audio synthesis system 602. In some embodiments,instructions executed by and/or data structures stored in sub-moduleswithin virtual audio synthesis system 602 may communicate with othercomponents of virtual audio synthesis system 602 (e.g., withinstructions executed by and/or data structures stored in othermodules).

In some embodiments, virtual audio synthesis system 602 may includegeneric model module 604. In some embodiments, generic model module 604may be used to synthesize virtual sounds for any virtual objects and/orcollisions between virtual objects and/or real objects. Generic modelmodule 604 may include known properties sub-module 610.

In some embodiments, known properties sub-module 610 may include one ormore data structures (e.g., a database) representing known materialproperties for common materials. For example, known propertiessub-module 610 may include absorption coefficients, diffusioncharacteristics, isolation characteristics (e.g., sound transmissionclass, noise criterion level, noise reduction coefficient), Young'smodulus, compliance, physical absorption, albedo, brittleness, density,elasticity, fluidity, tension, stiffness, strength, and/or boiling pointfor materials like concrete, brickwork, plaster, ceramic, plasterboard,glass, plywood, wood paneling, fiberglass, cork, marble, carpet, and/orother materials or variations of materials. In some embodiments, knownproperties of materials can be stored locally on a MR system. In someembodiments, known properties of materials can be stored on a remoteserver and retrieved by a MR system. In some embodiments, knownproperties sub-module 610 may include one or more data structures (e.g.,a database) representing properties of virtual and/or real environments.In some embodiments, properties of virtual and/or real environments canbe determined by a MR system (e.g., by firing an impulse response viaspeakers and receiving the response via microphones). In someembodiments, properties of virtual and/or real environments can bedetermined by other MR systems and uploaded to a remote server which maybe accessed by MR systems.

In some embodiments, virtual audio synthesis system 602 may be able toreceive and/or determine properties of virtual objects (e.g., at knownproperties sub-module 610). For example, an application or an objectdatabase may provide properties of a virtual object to a virtual audiosynthesis system. In some embodiments, a 3D mesh of a virtual object canbe provided to virtual audio synthesis system 602, which may allowvirtual audio synthesis system 602 to model the virtual object'sgeometry. In some embodiments, properties associated with a virtualobject (e.g., a material composition) may be passed to virtual audiosynthesis system 602. In some embodiments, a collision between virtualobjects may be determined via a physics engine (e.g., Unreal or Unity).In some embodiments, a physics engine may provide properties of avirtual object (e.g., a speed of a virtual object, impact forces, etc.)to virtual audio synthesis system 602.

In some embodiments, generic model module 604 may include observedproperties sub-module 612. Observed properties sub-module 612 may storeand/or determine properties of virtual and/or real objects that may notbe found in known properties sub-module 610. For example, a MR systemmay be able to automatically determine properties of real objects usingone or more sensors (e.g., one or more sensors of a MR system). In someembodiments, one or more optical cameras mounted on a MR system (e.g.,MR system 112, 200) may observe and identify a real object usingcomputer-vision methods. Visually observable properties (e.g., a colorand/or a patterning) may allow a MR system to determine a materialcomposition of the real object. In some embodiments, one or more depthcameras mounted on a MR system (e.g., MR system 112, 200) may be used todetermine density of the real object. In some embodiments, one or moremicrophones mounted on a MR system may record audio signals of a realobject interacting with other real objects. In some embodiments, opticalcameras and/or depth cameras (e.g., time-of-flight cameras) may observea velocity of a real object. In some embodiments, optical cameras and/ordepth cameras may allow a MR system to determine a collision between avirtual object and a real object (e.g., using simultaneous localizationand mapping (“SLAM”)). Other suitable sensors of a MR system may also beused to determine properties of real objects to accurately modelacoustic characteristics of those objects. Observed propertiessub-module 612 may also store and/or determine properties of a virtualand/or real environment.

In some embodiments, generic model module 604 may include model editorsub-module 614. Model editor sub-module 614 may allow a user to manuallyedit properties (e.g., properties stored in known properties sub-module610 and/or observed properties sub-module 612). For example, a user maymanually define and/or edit aspects of a 3D mesh of a virtual object, ora user may manually specify a desired absorption coefficient to use invirtual audio synthesis. In some embodiments, a user may manually editproperties using a graphical user interface (“GUI”), which may beprovided by model editor sub-module 614. In some embodiments, modeleditor sub-module 614 can provide one or more presets, which maycorrespond to common and/or known real and/or virtual objects. Forexample, model editor sub-module 614 can include a ping pong ballpreset, which may have acoustic properties of a ping pong ball that havebeen empirically determined and/or previously analytically determined.Model editor sub-module 614 can be an engine plug-in (e.g., a physicsand/or a game engine), a standalone application, and/or a web authoringtool.

In some embodiments, virtual audio synthesis system 602 may include aspecialized model module 606. Specialized model module 606 may storeand/or retrieve known acoustic models for real and/or virtual objects.Known acoustic models for real and/or virtual objects may be morecomputationally efficient and/or accurate to use than a model developedfrom scratch (e.g., using observed and/or known properties). Forexample, an 88-key piano may have a known acoustic model of how avirtual and/or real piano should sound that takes as input which key isplayed and how hard the key is struck. The known acoustic model may bemore efficient and/or accurate than physically modeling hammers, actionframes, tuning pins, strings, and/or a soundboard of an 88-key piano. Insome embodiments, known acoustic models may be retrieved from a remoteserver. In some embodiments, a MR system may develop an acoustic modelfrom scratch and upload the acoustic model (which may be associated witha virtual and/or real object) to a remote server, which may be retrievedby a MR system.

In some embodiments, virtual audio synthesis system 602 may includeparametric module 608. Parametric module 608 may synthesize virtualsounds using physical and/or non-physical parameters. For example, itmay be desirable to synthesize virtual audio according to a parameter ofhow far a user has progressed in a game level. In some embodiments,parametric module 608 may synthesize virtual audio that may notoriginate from a collision. For example, parametric module 608 maysynthesize virtual sounds originating from a car engine. Parametricmodule 608 may take as input parameters like engine load, RPM, and/orvehicle speed to synthesize virtual sounds. In some embodiments,parametric module 608 may modify and/or affect virtual soundssynthesized by other modules (e.g., generic model module 604 orspecialized model module 606). For example, a virtual sound originatingfrom a collision may be modified in amplitude by how far a user hasprogressed in a game level. In some embodiments, parametric module 608can include arbitrary excitation functions, resonators, and/orsignal-processing components, which a user may use and/or combine toproduce procedurally generated audio.

FIG. 7 illustrates an exemplary virtual audio synthesis system 700,according to some embodiments. In some embodiments, virtual audiosynthesis system 700 may correspond to virtual audio synthesis system602. Input aggregator 706 may receive data from virtual world inputprocessor 702. Virtual world input processor 702 may receive and/ordetermine virtual object data, which may be relevant to virtual audiosynthesis (e.g., a material composition of a virtual object or a speedof a virtual object). In some embodiments, virtual world input processor702 can be a physics engine (e.g., Unity or Unreal), which may calculatephysical interactions between objects. In some embodiments, virtualworld input processor 702 can receive data from a physics engine. Forexample, virtual world input processor 702 may receive collision data,speed data, material composition data, geometry data, and/or other dataabout one or more virtual objects from a physics engine. In someembodiments, virtual object data can be received from a remote server.

In some embodiments, virtual world input processor 702 may receiveand/or determine virtual environment data. Virtual environment data caninclude properties of a virtual environment. For example, virtualenvironment data can include dimensions and/or a geometry of a virtualenvironment. In some embodiments, virtual environment data can include amaterial composition of surfaces (e.g., floors, walls) of a virtualenvironment. In some embodiments, virtual environment data can include aplacement of real and/or virtual objects within a virtual environment.In some embodiments, virtual environment data can include acousticproperties of a virtual environment, such as a reverberation time,reverberation delay, and/or a reverberation gain. In some embodiments,properties of a virtual environment may be passed to virtual world inputprocessor 702 (e.g., from a physics engine). In some embodiments,properties of a virtual environment may be determined by virtual worldinput processor 702 (e.g., a virtual world input processor may determinea reverberation time based on a geometry and/or material composition ofa virtual environment). In some embodiments, virtual environment datamay be received from a remote server.

In some embodiments, input aggregator 706 may receive data from realworld input processor 704. Real world input processor 704 may receiveand/or determine real object data, which may be relevant to virtualaudio synthesis (e.g., a material composition of a real object or aspeed of a real object). Real world input processor 704 may receive datafrom one or more sensors, for example, one or more sensors of a MRsystem (e.g., MR system 112, 200). For example, a MR system may includean optical sensor (e.g., a camera) that may observe visualcharacteristics of a real object. Real world input processor 704 maydetermine a material composition of a real object based on a color,visual pattern, and/or a visual texture of a real object. In someembodiments, a MR system may include a depth sensor (e.g., atime-of-flight camera) that may observe a real object's position inthree-dimensional space. Real world input processor 704 may determine aspeed of a real object based on depth data and/or optical data.

In some embodiments, real world input processor 704 may receive and/ordetermine real environment data. Real environment data can includeproperties of a real environment. For example, real environment data caninclude dimensions and/or a geometry of a real environment. In someembodiments, real environment data can include a material composition ofsurfaces (e.g., floors, walls) of a real environment. In someembodiments, real environment data can include a placement of realand/or virtual objects within a real environment. In some embodiments,real environment data can include acoustic properties of a realenvironment, such as a reverberation time, reverberation delay, and/or areverberation gain. In some embodiments, real world input processor 704may determine real environment data from one or more sensors (e.g., oneor more sensors of a MR system). For example, a microphone of a MRsystem may observe characteristics of audio signals in the realenvironment, and real world input processor 704 may estimate areverberation time for the real environment. In some embodiments, realworld input processor 704 may receive real environment data from aremote server.

Input aggregator 706 may receive and/or aggregate data (e.g., virtualand/or real object data) from virtual world input processor 702 and/orreal world input processor 704. In some embodiments, input aggregator706 can aggregate, store, and/or retrieve virtual and/or real objectdata in database 708. In some embodiments database 708 can include amaterials database, which may include a list of common and/or knownmaterials and corresponding acoustic properties (e.g., absorptioncoefficients; diffusion characteristics; isolation characteristics suchas sound transmission class, noise criterion level, noise reductioncoefficient; Young's modulus; compliance; physical absorption; albedo;brittleness; density; elasticity; fluidity; tension; stiffness;strength; and/or boiling point). In some embodiments, materials data canbe retrieved from a remote server and stored in a materials database.

In some embodiments, database 708 can include an environment database,which may include a list of known real and/or virtual environments andcorresponding acoustic properties (e.g., reverberation time,reverberation delay, reverberation gain, location-dependent magnitudeand/or phase responses, absorption coefficients, impulse responses,and/or energy decay relief/curve). In some embodiments, an environmentdatabase may retrieve data from a materials database based on a materialcomposition of the real and/or virtual environment. In some embodiments,environment properties can be retrieved from a remote server and storedin an environment database.

In some embodiments, database 708 can include an objects database, whichmay include a list of known real and/or virtual objects andcorresponding properties. For example, objects database may include aregulation-size soccer ball and its geometry, surface area, volume,material composition, elasticity, mass, and/or other properties. In someembodiments, an objects database may retrieve data from a materialsdatabase based on a material composition of a real and/or virtualobject. In some embodiments, object data can be retrieved from a remoteserver and stored in an objects database.

Database 708 may also include other databases, which may include datarelevant to synthesizing virtual audio. In some embodiments, a materialsdatabase, an environment database, and/or an objects database can beintegrated into a single database. In some embodiments, a materialsdatabase, an environment database, and/or an objects database can bemaintained as separate databases. In some embodiments, input aggregator706 may store data (e.g., data received from virtual world inputprocessor 702 or real world input processor 704) in database 708. Insome embodiments, input aggregator 706 may retrieve data stored indatabase 708. In some embodiments, database 708 can correspond to knownproperties sub-module 610 and/or observed properties sub-module 612.

Input aggregator 706 may pass data (e.g., relevant acoustical propertiesof real and/or virtual objects) to impact engine 710. In someembodiments, impact engine 710 may calculate how a real and/or virtualobject vibrates upon impact with another real and/or virtual object.Impact engine 710 may use three-dimensional Newtonian physics tosimulate an expected vibration pattern upon impact, which may determinecompressions and rarefactions of surrounding air, which may determine asound perceptible to a user. In some embodiments, impact engine 710 maycommunicate with database 712, which may include one or more excitersand/or generators. In some embodiments, known exciters and/or generatorscan be combined and/or used to efficiently model impact vibrations of areal and/or virtual object. In some embodiments, an exciter and/orgenerator can be represented by one or more functions defining aresponse to an exciter and/or generator.

Input aggregator 706 may pass data (e.g., relevant acoustical propertiesof real and/or virtual objects) to a resonator engine 714. In someembodiments, resonator engine 714 may calculate how a real and/orvirtual object vibrates after impact with another real and/or virtualobject. Resonator engine 714 may use three-dimensional Newtonian physicsto simulate an expected vibration pattern after impact, which maydetermine compressions and rarefactions of surrounding air, which maydetermine a sound perceptible to a user. In some embodiments, resonatorengine 714 may communicate with database 716, which may include one ormore resonators. In some embodiments, known resonators can be combinedand/or used to efficiently model impact vibrations of a real and/orvirtual object. In some embodiments, a resonator can be represented byone or more functions defining a response after an impact. In someembodiments, resonator engine 714 may communicate with database 718,which may include one or more known resonator models. In someembodiments, one or more real and/or virtual objects can have knowncorresponding resonator models that accurately and efficiently model howthe object resonates. For example, a piano may be accurately andefficiently modeled using one or more resonator functions that may besimpler than modeling the full physics of each component part of apiano. When a real and/or virtual object has a corresponding resonatormodel, resonator engine 714 may use the corresponding resonator modelinstead of modeling the physics of all component parts of the realand/or virtual object. In some embodiments, after resonator engine 714has modelled the Newtonian physics of an unknown real and/or virtualobject, the model may be stored in database 718 as a known resonatormodel. In some embodiments, database 718 may retrieve and provide knownmodel data to a remote server. In some embodiments, resonator engine 714and database 718 may correspond to specialized model module 606. In someembodiments, impact engine 710, database 712, resonator engine 714,and/or database 716 can correspond to generic model module 604.

Parametric engine 720 may receive data from impact engine 710 and/orresonator engine 714, which may provide a representation of how a realand/or virtual object vibrates during and after an impact with anotherreal and/or virtual object. In some embodiments, parametric engine 720may modify an expected physical response of a real and/or virtual objectusing one or more parameters. In some embodiments, parametric engine 720may use non-physical parameters, such as level progression in a game. Insome embodiments, parametric engine 720 may map one or more physicalparameters to other values. For example, a virtual and/or real object'sangular velocity for the purposes of virtual audio synthesis may bemapped to a force exerted on the object. In some embodiments, parametricengine 720 may modify and/or provide parameters that can be interpretedby an excitation and/or resonator function (e.g., an excitation functionfrom database 712 or a resonator function from database 716).

In some embodiments, parametric engine 720 can more efficiently modelchanging properties than a continuous ground-up approach. For example, agame of ping pong with a virtual ping pong ball may shrink the size ofthe virtual ping pong ball with each volley. In some embodiments, thesize of the virtual ping pong ball could be continuously fed throughimpact engine 710 and/or resonator engine 714 to determine the acousticproperties of the ping pong ball. In some embodiments, parametric engine720 may be able to parameterize the shrinking size to reachsubstantially the same result.

Synthesizer 722 can receive data from parametric engine 720, such asacoustic properties of a real and/or virtual object that may have beenparametrically modified. Synthesizer 722 may synthesize a virtual soundbased on data received from parametric engine 720. Synthesizer 722 maycommunicate with database 724, which may include synthesis methods.Synthesis methods can include oscillators (e.g., sine waves, trianglewaves, sawtooth waves, square waves), filters, amplifiers, envelopegenerators, and/or modulators (e.g., low-frequency oscillators, ringmodulators) to create one or more waveforms, which may be stackedtogether. Synthesis methods can also include time-domain modalanalysis-based synthesis, frequency-domain modal analysis-basedsynthesis, analytical physical modeling synthesis,finite-element-modeling-based physical modeling synthesis, analogmodeling synthesis, classical numerical synthesis (e.g., AM/FM,additive/subtractive, wave-terrain, granular, wavetable, concatenative,formant-wave-function), and/or filter objects (e.g., 1-pole, 1-zero,biquad, comb, delay line, allpass, waveshaper, compander, lowpass,highpass, bandpass, bandstop).

In some embodiments, synthesizer 722 can pass data (e.g., a synthesizedsound) to database 726, which can include synthesized sounds. In someembodiments, synthesizer 722 can pass data (e.g., a synthesized sound)to rendering engine 728. Rendering engine 728 may render a virtual soundaccording to a corresponding spatial positioning of a virtual soundsource. For example, a virtual sound source behind a user may causerendering engine 728 to render the virtual sound such that it appear tothe user to be coming from behind. In some embodiments, rendering engine728 may communicate with database 726, which may include synthesizedsounds and/or prerecorded/pre-generated sounds. In some embodiments,rendering engine 728 can provide data to actuator 730 (e.g., one or morespeakers) to present the virtual sound to a user.

FIG. 8 illustrates an exemplary process 800 for choosing an audio model,according to some embodiments. In some embodiments, process 800 canoccur in resonator engine 714. At step 802, it can be determined if aspecific audio model exists for a real and/or virtual object. In someembodiments, the determination can be based on an identifier (e.g., akeyword identifier or a unique identifier) associated with a real and/orvirtual object. In some embodiments, an identifier for a virtual objectmay be passed to resonator engine 714 (e.g., from virtual world inputprocessor 702, or from an application that created the virtual object).In some embodiments, an identifier for a real object can be determined(e.g., by real world input processor 704 using computer vision and/ormachine learning algorithms to identify a real object). If it isdetermined that a specific audio model exists for a real and/or virtualobject, a specific audio model corresponding to the real and/or virtualobject may be used at step 808 (e.g., a specific audio model stored indatabase 718). If it is determined that a specific audio model does notexist for a real and/or virtual object, an audio model can be generatedat step 804 using properties of the real and/or virtual object. At step806, the generated audio model can be used to simulate sound for thereal and/or virtual object.

FIG. 9 illustrates an exemplary process 900 for generating an empiricalaudio model, according to some embodiments. In some embodiments, process900 can be performed by model editor sub-module 614. It can bebeneficial to use an empirical audio model when an analytical model(e.g., a model based on Newtonian physics) may be infeasible (e.g., whenan object's geometry is sufficiently complex). In some embodiments, anofficial empirical model can be based on one or more different empiricalmodels formed from different observations.

Sensor 902 a can include an audio sensor (e.g., a microphone) that cancapture an audio signal produced by the object when it collides withanother object. A first empirical model can be generated based on datafrom sensor 902 a at step 904 a. Sensor 902 b can include an opticalsensor (e.g., a camera) or a process that can read a file containingthree-dimensional geometry (e.g., a process that can read a mesh file).A second empirical model can be generated based on data from sensor 902b at step 904 b. In some embodiments, a second empirical model can begenerated using finite-element modeling of an object geometry. Sensor902 c can include a motion sensor (e.g., an accelerometer) that cancapture vibrations of an object when it collides with another object. Athird empirical model can be generated based on data from sensor 902 cat step 904 c.

At steps 906 a, 906 b, and 906 c, the first, second, and third empiricalmodels can be tuned to each other and/or with respect to each other. Insome embodiments, the tuning process can be iterative between theempirical models. In some embodiments, the tuning process can bring themultiple empirical models in closer agreement (e.g., the empiricalmodels generated from different data can produce similar expectedvibrations for an object). At step 908, an official empirical model canbe generated based on the one or more individual empirical models. Insome embodiments, the official empirical model can be made available toother components of a virtual audio synthesis system (e.g., an officialempirical model may be stored in database 718 as a known model).Although three empirical models are shown, it is contemplated that anynumber of empirical models can be generated from different data,including two, or four or more. Including additional empirical modelsmay increase an accuracy of an official empirical model, but may alsoreduce the likelihood of convergence between the individual modelsand/or increase a computational load.

Although the disclosed examples have been fully described with referenceto the accompanying drawings, it is to be noted that various changes andmodifications will become apparent to those skilled in the art. Forexample, elements of one or more implementations may be combined,deleted, modified, or supplemented to form further implementations. Suchchanges and modifications are to be understood as being included withinthe scope of the disclosed examples as defined by the appended claims.

What is claimed is:
 1. A method comprising: determining a collisionbetween a first object and a second object, wherein the first objectcomprises a first virtual object; accessing a memory storing one or moreaudio models; determining if the one or more audio models stored in thememory comprises an audio model corresponding to the first object; inaccordance with a determination that the one or more audio modelscomprises an audio model corresponding to the first object: synthesizinga first audio signal, wherein the first audio signal is based on thecollision and the audio model corresponding to the first object, andpresenting the first audio signal, via a speaker of a head-wearabledevice, to a user; and in accordance with a determination that the oneor more audio models does not comprise an audio model corresponding tothe first object: determining an acoustic property of the first object,generating a custom audio model based on the acoustic property of thefirst object, synthesizing a second audio signal, wherein the secondaudio signal is based on the collision and the custom audio model, andpresenting the second audio signal, via the speaker of the head-wearabledevice, to the user.
 2. The method of claim 1, wherein the second objectcomprises a second virtual object.
 3. The method of claim 1, wherein thesecond object comprises a real object.
 4. The method of claim 3, furthercomprising: receiving, via a sensor of the head-wearable device, sensordata associated with the real object; determining an acousticcharacteristic of the second object based on the sensor data; andgenerating an audio model corresponding to the second object based onthe acoustic characteristic.
 5. The method of claim 3, furthercomprising: identifying, via a sensor of the head-wearable device, anaspect of the second object; retrieving an acoustic characteristic ofthe second object based on the identified aspect; and generating anaudio model corresponding to the second object based on the acousticcharacteristic.
 6. The method of claim 3, further comprising: receiving,via a sensor of the head-wearable device, sensor data associated withthe real object; determining a first acoustic characteristic of thesecond object based on the sensor data; generating a first audio modelcorresponding to the second object based on the first acousticcharacteristic; identifying, via a sensor of the head-wearable device,an aspect of the second object; retrieving a second acousticcharacteristic of the second object based on the identified aspect;generating a second audio model corresponding to the second object basedon the second acoustic characteristic; and generating a third audiomodel corresponding to the second object based on the first audio modelcorresponding to the second object and the second audio modelcorresponding to the second object.
 7. A system comprising: one or moreprocessors, wherein the one or more processors are configured to executea method comprising: determining a collision between a first object anda second object, wherein the first object comprises a first virtualobject; accessing a memory storing one or more audio models; determiningif the one or more audio models stored in the memory comprises an audiomodel corresponding to the first object; in accordance with adetermination that the one or more audio models comprises an audio modelcorresponding to the first object: synthesizing a first audio signal,wherein the first audio signal is based on the collision and the audiomodel corresponding to the first object, and presenting the first audiosignal, via a speaker of a head-wearable device, to a user; and inaccordance with a determination that the one or more audio models doesnot comprise an audio model corresponding to the first object:determining an acoustic property of the first object, generating acustom audio model based on the acoustic property of the first object,synthesizing a second audio signal, wherein the second audio signal isbased on the collision and the custom audio model, and presenting thesecond audio signal, via the speaker of the head-wearable device, to theuser.
 8. The system of claim 7, wherein the second object comprises asecond virtual object.
 9. The system of claim 7, wherein the secondobject comprises a real object.
 10. The system of claim 9, the methodfurther comprising: receiving, via a sensor of a head-wearable device,sensor data associated with the real object; determining an acousticcharacteristic of the second object based on the sensor data; andgenerating an audio model corresponding to the second object based onthe acoustic characteristic.
 11. The system of claim 9, the methodfurther comprising: identifying, via a sensor of the head-wearabledevice, an aspect of the second object; retrieving an acousticcharacteristic of the second object based on the identified aspect; andgenerating an audio model corresponding to the second object based onthe acoustic characteristic.
 12. The system of claim 9, the methodfurther comprising: receiving, via a sensor of the head-wearable device,sensor data associated with the real object; determining a firstacoustic characteristic of the second object based on the sensor data;generating a first audio model corresponding to the second object basedon the first acoustic characteristic; identifying, via a sensor of thehead-wearable device, an aspect of the second object; retrieving asecond acoustic characteristic of the second object based on theidentified aspect; generating a second audio model corresponding to thesecond object based on the second acoustic characteristic; andgenerating a third audio model corresponding to the second object basedon the first audio model corresponding to the second object and thesecond audio model corresponding to the second object.
 13. Anon-transitory computer-readable medium storing instructions that, whenexecuted by one or more processors, cause the one or more processors toexecute a method comprising: determining a collision between a firstobject and a second object, wherein the first object comprises a firstvirtual object; accessing a memory storing one or more audio models;determining if the one or more audio models stored in the memorycomprises an audio model corresponding to the first object; inaccordance with a determination that the one or more audio modelscomprises an audio model corresponding to the first object: synthesizinga first audio signal, wherein the first audio signal is based on thecollision and the audio model corresponding to the first object, andpresenting the first audio signal, via a speaker of a head-wearabledevice, to a user; and in accordance with a determination that the oneor more audio models does not comprise an audio model corresponding tothe first object: determining an acoustic property of the first object,generating a custom audio model based on the acoustic property of thefirst object, synthesizing a second audio signal, wherein the secondaudio signal is based on the collision and the custom audio model, andpresenting the second audio signal, via the speaker of the head-wearabledevice, to the user.
 14. The non-transitory computer-readable medium ofclaim 13, wherein the second object comprises a second virtual object.15. The non-transitory computer-readable medium of claim 13, wherein thesecond object comprises a real object.
 16. The non-transitorycomputer-readable medium of claim 15, the method further comprising:receiving, via a sensor of the head-wearable device, sensor dataassociated with the real object; determining an acoustic characteristicof the second object based on the sensor data; and generating an audiomodel corresponding to the second object based on the acousticcharacteristic.
 17. The non-transitory computer-readable medium of claim15, the method further comprising: identifying, via a sensor of thehead-wearable device, an aspect of the second object; retrieving anacoustic characteristic of the second object based on the identifiedaspect; and generating an audio model corresponding to the second objectbased on the acoustic characteristic.
 18. The non-transitorycomputer-readable medium of claim 15, the method further comprising:receiving, via a sensor of the head-wearable device, sensor dataassociated with the real object; determining a first acousticcharacteristic of the second object based on the sensor data; generatinga first audio model corresponding to the second object based on thefirst acoustic characteristic; identifying, via a sensor of thehead-wearable device, an aspect of the second object; retrieving asecond acoustic characteristic of the second object based on theidentified aspect; generating a second audio model corresponding to thesecond object based on the second acoustic characteristic; andgenerating a third audio model corresponding to the second object basedon the first audio model corresponding to the second object and thesecond audio model corresponding to the second object.